Technical Field
The present disclosure relates to a hydrogenation reactor and process for removing unsaturated impurities from olefins and oxygenates.
Technical Background
The selective hydrogenation of alkynes is an integral process in the purification of olefin and oxygenate streams. Acetylenic and diolefinic impurities are inevitably present in such streams and should be removed or reduced to prevent catalyst poisoning and to meet target specifications for the downstream production of fine chemicals and polymers. For example, ethylene streams can typically comprise from about 0.1 to 3 mole % of acetylene, and propylene streams can typically comprise from about 0.5 to 10 mole % of propyne and/or propadiene. Ideally, the concentration of these acetylenic impurities should be reduced to levels of about 0.5 mole % or less and propyne and/or propadiene level should be less than 2.8 mole %.
Conventional processes for the hydrogenation of acetylene utilize a catalyst, such as a Pd-based catalyst that is modified with promoters. The generally accepted mechanism for acetylene hydrogenation is that acetylene adsorbs on the palladium metal sites on the catalyst, and then reacts with hydrogen. The availability of active palladium sites for the adsorption of acetylene impacts the selectivity of the catalyst. While hydrogenation of ethylene to ethane intrinsically occurs at a faster rate, the selective adsorption of acetylene on palladium can result in efficient acetylene hydrogenation if a sufficient quantity of acetylene exists to adsorb to active palladium metal sites.
Low concentrations of carbon monoxide can also be utilized as a reaction modifier in front-end acetylene converters. Carbon monoxide adsorbs to palladium more strongly than acetylene or conjugated diolefins, so it can prevent the adsorption of ethylene at even low concentrations.
Disadvantages of such hydrogenation/dehydrogenation processes include the production of alkanes, oligomers, and the formation of coke. In conventional high space velocity and low contact reactions (e.g., hydrogenation and dehydrogenation), uniform feed distribution and low pressure drops are desirable. Runaway reactions and hotspots that can affect production rates and selectivity are also common.
Accordingly, there is an ongoing need for new, efficient reactors and processes for hydrogenation and dehydrogenation reactions, such as for example, in processes for removing unsaturated impurities from olefins and oxygenates. These needs and other needs are satisfied by the compositions and methods of the present disclosure.